Influence of plant size on female-biased sex allocation in a single-flowered, nectarless herb.

Ying-Ze Xiong,Shuang-Quan Huang,Meng Xie

doi:10.1093/aobpla/plv139

Ying-Ze Xiong, Shuang-Quan Huang + Show 1 more

Open Access

https://doi.org/10.1093/aobpla/plv139

Copy DOI

Abstract

Relative allocation to female and male function in hermaphroditic species often departs from strict equisexuality. Increased femaleness with plant size in animal-pollinated species has been proposed in theory and demonstrated in empirical studies. However, such size-dependent sex allocation (SDS) has not been observed in some insect-pollinated species, throwing doubt on the generalization of SDS, that large plants have decelerated male function investment. Himalayan mayapple Podophyllum hexandrum (Berberidaceae) produces a single terminal flower and no nectar, providing a simple system for studying SDS without the confounding effects of flower number and nectar production. To investigate the SDS in P. hexandrum, plant size, biomass of floral organs (stamens, pistils and petals) and gamete production (pollen and ovule number) were measured in four populations in Yunnan Province, northwest China. Isometric allocation to female and male function with plant size was found in two populations, but the prediction of SDS was supported in the other two populations. Using pollen and ovule production as the allocation currency, allocation to female and male function was isometric in all studied populations. Resources allocated to attractive (petals) and sexual (pistils and stamens) structures did not show a significantly disproportionate increase with plant size in three of the four studied populations. The general pattern of isometric allocation to female and male function and to attractive and sexual structures could be attributed to the species being capable of automatic self-pollination, related to low pollen loss, minor deleterious effect of selfing and low importance of attractive structures. However, in further studies, careful consideration should be given to the different currencies used to estimate sex allocation.

Highlights

The theory of sex allocation proposes that co-sexual plants should allocate equal resources to female and male function if the fitness returns of relative investment into these two functions are equal (Charnov 1982; de Jong and Klinkhamer 2005)
To examine whether size-dependent sex allocation (SDS) occurs and varies in different populations of Himalayan mayapple, here we address three questions: (i) Does resource allocation to femaleness and maleness increase with plant size? (ii) Is sex allocation to female and male functions with plant size isometric or allometric? (iii) Does SDS vary across populations?
The dry weight of floral organs correlated with each other (Table 2) and all were significantly positively related with plant size

Summary

Introduction

The theory of sex allocation proposes that co-sexual plants should allocate equal resources to female and male function if the fitness returns of relative investment into these two functions are equal (Charnov 1982; de Jong and Klinkhamer 2005). Xiong et al — Sex allocation in mayapple with plant size (see Lloyd and Bawa 1984; Bickel and Freeman 1993; Klinkhamer et al 1997). Since female function involves more resource cost to produce seeds, female-biased sex allocation with plant size should be more common under resource limitation condition (sex-differential resource costs, Lloyd and Bawa 1984; Bickel and Freeman 1993; Day and Aarssen 1997). Resource condition could play an important role in affecting relative allocation to female and male function

Methods

Results

Discussion

Conclusion